A process is well known in the art for growing diamonds under pressures and at temperatures corresponding to its thermodynamic stability in the carbon-metal system. In the state diagram of graphite-diamond the range of working pressures is above the equilibrium line for graphite-diamond (range of thermodynamic stability of diamond), wherefore the range of growing temperatures is limited, on the one hand, by the metal melting curve and, on the other hand, by the equilibrium line. In the chamber of a solid-phase high-pressure unit, pressure is created and a container made of an elasto-plastic material (such as lithographic stone) with a reaction space volume of from 1.0 to 3.0 cm.sup.3 is placed thereinto. In the reaction space there is present graphite or any other carbonaceous substance and metal-catalyst-solvent. Heating is effected by passing electric current directly through the reaction space on a special heater provided therein. In one of the embodiments the known process stipulates the creation of high temperatures and pressures necessary for the synthesis of diamond within the range of its thermodynamic stability (cf. U.S. Pat. No. 3,124,422, published in 1964).
In this embodiment of the prior art process for growing diamonds the residence of the growth system in the stage of thermodynamic stability of graphite at a temperature exceeding the melting point of the metal-solvent-catalyst is accompanied by the formation of a graphite phase capable of initiating the process of recrystallization of metastable graphite within the range of thermodynamic stability of diamond so as to compete with the diamond-formation process, thus hindering the formation of substantially large (above 0.4 mm) fractions of diamond crystals and limiting the yield of these fractions to 13-15%.
Also known in the art is a process for growing diamonds, wherein, unlike in the above-described process, into the growth system there are added active compounds-nitrides of such metals as titanium, zirconium, hafnium, vanadium, boron, and silicon (see Japanese Pat. No. 4605, published in 1972).
The addition of said active substances contributes to a certain increase in the yields of large size fractions of diamond crystals. However, this increase is limited to several percent of the total weight of the synthesized crystals. The stable yield of large-size (above 0.4 mm) fractions of diamond crystals is, in the discussed embodiment of the process, not more than 20% which is insufficient for their industrial manufacture.